1. Field of the Invention
The present invention relates to devices that automatically supply water to a steam boiler when the water level is low. More specifically, the present invention relates to water feeders for steam boilers of the type used in residential and light commercial heating applications that include a low water cutoff sensor to turn off the burner when the water is below the sensor.
2. Description of Related Art
In conventional boilers of the type used in residential and light commercial heating the water level is monitored with a low water cutoff sensor. When the water level in the boiler drops below the level of the low water cutoff sensor, the burner is turned off until the water level is brought back up to a safe level.
One method of adding water to this type of steam boiler is with an automatic water feeder, which controls a feed valve to supply water to the boiler. When the cutoff sensor senses a low water condition, it stops the burner from firing, and transfers power to the water feeder, allowing it to add make-up water. When the low water cutoff sensor detects that the water level has reached a safe level, it transfers power back to the burner, allowing it to restart and correspondingly disables the water feeder by removing its power.
In conventional water feeder designs of this type, the water feeder is disabled by the low water cutoff sensor as a result of the transfer of power away from the feeder to the burner. Thus the water feeder cannot feed water to the boiler after the burner is re-enabled. One type of low water cutoff sensor uses a float in the boiler, which mechanically drives a switch to transfer power between the burner and the water feeder. In this type of design, the power transfer occurs instantly, as the water level reaches a height sufficient for the float to operate the switch.
Another type low water cutoff sensor uses an electronic probe. With a probe-type electronic sensor, the transfer of power back to the burner can be delayed slightly, allowing a limited amount of additional water to be added above the probe level. However, because the same low water cutoff probe may be used on boilers of various sizes, this delay cannot be too long, as the water feeder cannot be allowed to feed an excess of water into a small boiler.
Water feeders currently available incorporate two timing circuits. The first timer (delay timer) provides for a delay period before the feed valve is activated. This delay allows time for steam within the heating system to condense to water and return to the boilerxe2x80x94thus ensuring that make-up water is required. If the low water cutoff sensor detects that the water level has returned to a safe operating level during the delay period, then no additional water is added and the cutoff sensor re-enables the burner allowing the boiler to operate normally.
The second timer (feed timer) controls the feed valve and adjusts the maximum time that the feeder will supply water to the boiler. After the delay timer has timed out, it triggers the feed timer, which operates the feed valve and begins supplying water to the boiler. When the water in the boiler reaches the low water cutoff sensor, the burner is re-enabled, the feed valve is turned off and the cycle repeats. The feed timer limits the maximum time that water feeding can occur during a feed cycle. Adjustable settings are provided on water feeders to accommodate boilers with different designs and different feed requirements. The best current water feeder designs also include a manual feed override to manually fill the boiler and a lockout feature to prevent the water feeder from cycling/feeding indefinitely in the event of a malfunction of the low water cut-off sensor.
One significant problem with current water feeder designs is that they provide no means for determining how much water has been added to a boiler. Introducing tap water to a boiler too frequently can shorten the life of the boiler. Over time, oxygen rich tap water can rust a cast iron boiler at the water line. Additionally, unwanted and potentially harmful elements, such as lime, can enter the boiler during each feed cycle. If there is a leak in the system, excess deposits can build up in the boiler and produce a layer of material at the bottom of the boiler. This layer typically has poor heat transfer characteristics and can result in the boiler cracking during heating. A water feeder having a display of the amount of water supplied by the water feeder is desirable to allow the owner or installer to determine if the boiler is operating normally, with normal water losses, or if water is leaking from the system, producing rapid water loss.
Another problem with current water feeder designs resides in the fact that the water feeder receives its power from the low water cutoff sensor, which transfers power from the burner to the feeder when the water level is low and removes power from the water feeder as soon as the water level reaches the cutoff sensor. In this type of design the low water cutoff sensor will stop the water feeder during the feed cycle when the level of the water is at or near the level of the cutoff sensor.
Regardless of the duration of the feed timer, the feeder can only fill to approximately the level of the cutoff sensor. While the low water cutoff sensor is installed in the boiler at a safe operating level, it is generally well below the optimum water level for operating the boiler. As a result, boiler operation with a conventional water feeder installed is less efficient than if the boiler were manually filled to operate at a higher water level in accordance with the manufacturer""s recommendations.
One solution to this problem has been to use an upper water level sensor to determine when the water feeder has supplied enough water to reach the upper sensor level. The upper sensor is installed above the optimum water level. However, because an upper sensor must be installed at the time the boiler is constructed, and such a sensor increases costs, most boiler manufacturers do not install such a sensor. Consequently, this solution is not suitable for existing boiler installations.
To alleviate this problem installers in the field have made modifications to conventional water feeders by mounting a latching relay near to the water feeder and rewiring the connection between the low water cutoff sensor and the power wiring to the water feeder. The latching relay is installed to supply power to the water feeder after the low water cutoff sensor is satisfied and after the cutoff sensor attempts to remove power from the feeder. This field modification allows the feeder to complete a full feed timer cycle every time and bring the water level above the cutoff sensor. However, field modifications of existing designs are inconvenient at best and require additional installation work. An integrated water feeder design capable of supplying water to above the level of the low water cutoff sensor is desired by the industry.
Bearing in mind the problems and deficiencies of the prior art, it is therefore an object of the present invention to provide a water feeder controller for a boiler having a display for indicating the quantity of water supplied by the water feeder to the boiler.
It is another object of the present invention to provide a water feeder controller for a boiler in which the water feeder raises the water level in the boiler well above the low water cutoff level during the fill cycle and completes an entire predetermined feed cycle during each feed period to add a known quantity of water to the boiler each cycle.
A further object of the invention is to provide a water feeder controller for a boiler that can fill well above the level of the low water cutoff sensor, without requiring a second sensor to detect a water level above the low water cutoff sensor.
Still other objects and advantages of the invention will in part be obvious and will in part be apparent from the specification.
The above and other objects, which will be apparent to those skilled in art, are achieved in the present invention, which is directed to a water feeder controller for a boiler that monitors a low water cutoff sensor in a boiler and uses a feed timer to feed water to the boiler for a predetermined feed period of time. The feed timer continues to feed water for a full feed cycle to bring the water level in the boiler above the low water cutoff sensor. The feed timer supplies water to the boiler only if the low water cutoff sensor continues to indicate a low water level for a delay period of time measured by a delay timer. A display indicates the quantity of water supplied by the water feeder to the boiler based on a feed counter incremented during water feeding. A manual feed button allows water to be manually fed to the boiler. The quantity of water manually supplied to the boiler is also shown on the display. The feed timer and delay timer are preferably implemented in software in a microcontroller in the water feeder controller. A lockout loop in the software prevents overfeeding of water to the boiler in the event of a failure of the low water cutoff sensor.
More specifically, the invention is directed to a water feeder controller for a boiler that includes an input for receiving a low water signal from a sensor in the boiler, an output for connection to a feed valve capable of supplying water to the boiler at a predetermined feed rate, a delay timer having a delay timer period, a feed counter, a feed timer having a feed timer period and a display.
The delay timer is connected to the input to begin timing for the delay timer period responsive to the low water signal from the sensor. The feed timer is connected to the delay timer to begin timing for the feed timer period after the delay timer period. The feed timer is also connected to the output to turn on the feed valve during the feed timer period, and the feed timer is further connected to the feed counter to increment the feed counter during the feed timer period. The display is connected to the feed counter to display a number corresponding to the quantity of water supplied by the feed valve to the boiler.
The water feeder controller preferably includes a display reset button and a manual feed button. The display reset button is connected to reset the feed counter and thereby reset the display to a zero quantity of water supplied by the feed valve to the boiler. The manual feed button is connected to open the feed valve when it is pressed and is also connected to increment the feed counter as water is being fed to the boiler.
In one aspect of the invention, the water feeder controller includes a microcontroller and the delay timer, the feed timer and the feed counter are all implemented in software in the microcontroller. In the preferred embodiment of this design, the delay timer and feed timer include corresponding delay and feed loops in the software wherein the delay and feed loops repetitively cycle through program steps of the software during the corresponding delay and feed periods of the delay and feed timers.
In the preferred design, the delay loop includes a program step for checking the input to detect the low water signal. The software exits the delay loop without starting the feed timer if the sensor indicates the presence of sufficient water in the boiler during the delay period. When the water feeder is provided with a manual feed button, it is preferred that the delay loop include a program step for determining if the manual feed button has been pressed during the delay period. When the water feeder is provided with a display reset button, it is preferred that the delay loop also include a program step for determining if the display reset button has been pressed during the delay period.
The feed loop includes a program step for determining if the feed loop has been cycling for the feed period and then passes program control to a reset loop. The reset loop includes a program step for checking the input to detect the low water signal. The reset loop starts the delay timer if the sensor indicates a low water level in the boiler. When the water feeder is provided with a manual feed button, it is preferred that the feed loop include a program step for determining if the display reset button has been pressed during the feed period. The feed loop includes a program step for incrementing the feed counter to track water usage.
To prevent the water feeder controller from overfeeding water to the boiler, the software includes a program step for stopping the feed timer from repetitively turning on the feed valve. This is achieved with a program step for checking the number of times the feed timer has been sequentially started. If the number of times the feed timer has been sequentially started exceeds a desired value, program control passes to a lockout loop. The lockout loop prevents the feed timer from being restarted.
In the most highly preferred design, the lockout loop includes a program step for checking the input to detect the low water signal. The software then exits the lockout loop if the sensor indicates the presence of sufficient water in the boiler. This ensures that the low water sensor is functioning.
The invention is also directed to a method of controlling a water feeder for a boiler comprising the steps of:
receiving a low water signal from a sensor in a boiler, the low water signal indicating the presence or absence of sufficient water in the boiler;
delaying for a delay period of time after receiving the low water signal;
checking the low water signal after the delay period;
feeding water to the boiler for predetermined feed period of time if the low water signal indicates insufficient water in the boiler after the delay period; and
displaying the quantity of water supplied to the boiler based on the period of time water is fed to the boiler.